Add signatures to all stub files

[Matthijs]

I notice it is a recurring source of annoyance to me that I have to figure out the signatures myself. Not seeing any real benefit to omitting them, I propose to add them to all stub files.

I'm prepared to do this myself; I'm opening this issue in the hope of hearing your thoughts.

[Emiel van de Laar]

Thanks for reaching out @MatthijsBlom. I think this is reasonable and I see other languages do this as well:

• https://github.com/exercism/haskell/blob/main/exercises/practice/hello-world/src/HelloWorld.hs
• https://github.com/exercism/fsharp/blob/main/exercises/practice/hello-world/HelloWorld.fs

Feel free to start on a pull request.

I suppose it would be nice that the stub builds and raises an error indicating the function needs to be implemented. Something along the lines of: https://github.com/exercism/haskell/blob/main/exercises/practice/bob/src/Bob.hs

[Matthijs]

Great. I'll get started on a PR sometime in the near future.

I suppose it would be nice that the stub builds and raises an error indicating the function needs to be implemented.

Yes. I see four options:

• Use ?todo, which raises a compile error, which is 👍, but also prevents a successful build, which is 😢.
• Use crashWith, which requires Partial 👎 and thereby breaks the build 😢.
• Use Undefined.undefined, which allows for build 👍 but results in an inscrutable runtime error 👎.
• Use unsafeThrow, which allows for build 👍 and gives a slightly better runtime error 🤷.

In my experience a successful build is important to get the language server going, so I guess we should go with unsafeThrow and accept its short-lived import and normalization of unsafe.